Have structural questions? You're not alone. Black Box has compiled a growing list of frequently asked questions related to existing building modifications, buying property, DOB regulations, new construction, and other structural-related projects. Make sure to check back regularly for new inquiries! Can't find your question below? Reach out to us here.

Structural FAQs

Why are my outdoor metal finishes (railings, steel beams, canopies, pipe fittings) rusting?


Rusting is a form of oxidation which is a slow but inevitable chemical reaction between iron and oxygen. When metal elements are left outside and exposed to the weather, this reaction speeds up dramatically. In addition to being an eyesore, rust eats away at the steel over time and reduces its structural capacity, which over time could potentially have catastrophic consequences. Avoiding rust is a simple solution but requires foresight and planning. During the design process, any metal components exposed to the weather should be specified to be weather-resistant; stainless steel elements should be selected when possible, and structural steel should be hot-dip galvanized in the shop prior to arriving on site. If your existing steel is already exhibiting rust, some solutions can include spray galvanization, or the application of weather-resistant paints (after removing the rust). Hot-dip galvanization and stainless steel pieces will always be more expensive than their untreated counterparts upfront, however, post-installation solutions such as painting or spray galvanization must be re-applied periodically, which could end up costing more in the long run. Rusting dunnage ( mech. unit support) beams




I'm pouring less than 50 cubic yards of concrete. Do I need a cast-in-place concrete special inspection?


Yes, any quantity of cast-in-place concrete requires a special inspection, except for foundations of lightweight fences, sidewalks, patios, driveways, or any other small outdoor non-structural slabs based on Section 1704.4 of the NYC Building Code. If you're pouring less than 50 cubic yards of concrete for the entire project (about 5 full concrete trucks), or pouring foundations for standard one or two-family homes, the special inspection does not require the concrete to be sampled; this means no cylinders need be taken for independent lab testing, and the TR2 and TR3 forms are not required for filing. This exception must be stated by the design applicant in the project's general notes. Building codes outside of NYC hold similar requirements. Without the sampling requirement, the special inspector is still required to review the reinforcement, concrete mix, and all other components of the concrete element prior to pouring.




My floors are sagging. Is this dangerous? What can I do?


Not always. In NYC, this problem is most commonly observed in detached houses, rowhouses, and brownstones. Almost all homes exhibiting this issue were built between 1890 and 1940 using wood floor joists. At the time, these floors were not designed with deflection or sagging in mind, so generally all floors in these properties will have developed some level of sag over time. Most homeowners never realize or see this unless they rip open their ceilings or floors (usually done for gut renovations). The floor joists that show the most damage are typically below bathrooms (due to rot caused by water damage) and at stairs (due to high concentrated loads). What you can do: For the most part, floor joists cannot be assessed by a structural engineer or home inspector without opening up portions of or the entire ceiling. If joists are found in poor condition, a short term solution could be to reinforce the floor from below to prevent further sagging. Long-term solutions include sistering (coupling) the existing joist with a new joist, or replacing the joist entirely, however, this is never a simple solution. Straightening floor joists have multiple consequences; as the floors have sagged over time, so has everything else in the home on top of it. So straightening a floor will push up the floor finishes, walls, etc., which could cause many finishes to crack. In conclusion, straightening a sagged floor should only be done under the direction of a competent structural engineer and recommended mostly for gut renovations, where all finishes and interior (non-load bearing) walls can be removed and replaced.




I'm making structural modifications to my property. Do I need a geotechnical report (TR4)?


For NYC projects: According to section 1802.2 of the NYC Building Code, geotechnical reports are required for new building construction, horizontal enlargements of an existing building, vertical enlargements of an existing building where new foundations are required, or vertical enlargements where existing foundations are receiving new loads greater than 5% of the existing capacity. The number of test pits and borings that are required depend on the outlined area of new foundation elements, which are listed in section 1802.4.1 of the NYC Building Code, with an exception to substitute borings for test pits for one and two-story structures. For projects outside of NYC: Based on the International Building Code, which most counties follow, geotechnical investigations are required for almost any scenario where new foundations are being poured, or when requested by county officials or the Engineer of Record (EOR). This requirement can sometimes be waived by county officials if satisfactory geotechnical data is available from an adjacent lot or area. Black Box does not perform geotechnical reports; please contact us if you need a referral!




What is the difference between class 1 and class 2 special inspections (NYC)?


The NYC Department of Buildings categorize special inspection agencies (businesses that can perform special inspections) into three classes, as explained on their website. Class 1 agencies can perform special inspections for any building or construction type. Class 2 agencies can perform special inspections for new construction, full demolition, or alterations of non-major buildings. A non-major building is defined by the DOB (in section 3302.1 of the Building Code) as: an existing or proposed building that is less than 10 stories in height and has a building footprint less than 100,000 square feet, and is not designated by the DOB as a "major building" due to unique hazards associated with the demolition or construction of the structure. Class 2 agencies can also perform special inspections for alterations to major buildings given the following:

  • Alterations do not exceed the removal of one whole story or more,
  • partial demolitions do not exceed 20,000 square feet nor 20% of gross floor area, or
  • horizontal or vertical enlargements do not exceed more than 10,000 square feet of gross floor area.
Class 3 agencies can perform special inspections only for the construction, demolition, or alteration of a on-, two-, or three-family dwelling, or the alteration or demolition of any building of less than 10,000 square feet of gross floor area. Black Box is currently a class 2 special inspection agency.




Is my wall load-bearing?


That is a loaded question (no pun intended)! A competent structural engineer with existing building experience would be able to make some accurate assumptions on the load-bearing condition of a wall based on the type of building, location of the wall in the building, geographical location of the building, and the time period the building was built. However, there are many cases (especially with wood-frame houses or newer buildings) that designs are unique to the structure and further structural assessment is required. The easiest (and non-destructive) way for a structural engineer to determine if a wall is load-bearing or not is to check the existing building drawings, or the "blueprints". Unfortunately these are often unavailable or no longer exist. If this is the case, and the structural engineer cannot make an assessment based on prior experience, then probing would be the next option. Probing typically includes opening a small portion of the ceiling and/or wall to take a look at the intersection of the floor joists and wall studs to make an assessment. Below are some rules of thumb structural engineers use to determine a load-bearing condition. Please note there are exceptions to every rule. The following should not be taken as structural consultation; always consult a structural engineer directly prior to assuming the load-bearing condition of any wall:

  • Perimeter or exterior walls are typically load-bearing.
  • Brick or solid concrete walls are typically load-bearing.
  • Load-bearing walls typically continue down to the base or foundation of the home or building.
  • A wall that runs perpendicular to the direction of the floor joists are typically load-bearing to some degree (but not always).
Whether your wall is load-bearing or not, partial or full-removal often has consequences. A structural engineer should be consulted prior to any wall removal project.




Can I convert my existing building's roof to a roof terrace?


If you're a building owner in New York City and have asked this question, you are not alone! The short answer is yes, but doing so is a much more complex solution than one would expect. From a structural standpoint, older buildings that have nothing but roofing material on their roofs were typically designed to resist minimal loading from the occasional maintenance worker or wanderer, and therefore normally do not have the structural capacity to support a new terrace or occupied space. Below are a few methods structural engineers use to determine if a roof has the structural capacity to resist new terrace loading:

  1. Checking the Certificate of Occupancy, sometimes referred to as the "C of O". Certificates of occupancy show the live load that buildings were designed to sustain per floor. This is an excellent indicator to the structural engineer whether or not heavier loading can be supported. Certificates of Occupancy can be found in the NYC Department of Buildings "Building Information Search (BIS)" system by plugging in the property address. Unfortunately, certificates of occupancy are often missing or do not include loading information for unoccupied roofs of older properties
  2. Checking existing building drawings, or the "blueprints". These documents are often unavailable or no longer exist.
  3. If the certificate of occupancy and existing drawings are missing or incomplete, a probe can be performed (applicable only to buildings with wood floor joists). A probe consists of opening a portion of the ceiling below the roof to determine the size and spacing of the roof joists.
If the roof is determined to be structurally inadequate for new terrace loading after structural analysis, joist reinforcement would be required. This can practically only be done by removing the entire ceiling below during a partial or full gut renovation. The presence of asbestos or insulation often complicate these types of projects. Apart from structural capacity, there are many other factors involved in converting an unoccupied roof space to an occupied roof terrace, which include zoning, egress and accessibility, fire code compliance, occupancy limitations, etc. The NYC Department of Buildings released a helpful (but technical) document providing guidance on code-specific regulations and limitations for rooftop conversions: Buildings Bulletin 2018-002. If you're looking to convert your rooftop space, consult with a competent architect first to gain an understanding of your building's specific limitations and requirements.




I'm building (or rebuilding) a house. Do I need a structural engineer?


First let's define "house". In this context, a house is defined as a detached one- or two-family dwelling not more than three stories above ground level. If you're building a standard home out of wood or light-gage joists, you usually do not need a structural engineer. However in special cases, there may be some scenarios where your primary design applicant (usually an architect) will consult a structural engineer. If you're looking to build (or rebuild) a home, the first step is to hire an architect. Think of the architect as the quarterback of your homebuilding project; they are responsible for laying out the home and ensuring compliance of that layout with the applicable building codes. For standard homebuilding projects, architects also typically cover structural, electrical, mechanical, and plumbing details. However, when the project is complex or when the architect lacks experience with one of the above-mentioned trades, they hire a structural or mechanical engineer to assist in developing the drawings. For architects: The NYC building Code and the International Building Code both provide sizing tables for conventional light-frame construction; see Section 2308 of the NYC Building Code. The International Building Code also provides tables for prescriptive foundation wall design; see Section 1807 . Consult with a structural engineer if you need assistance reading the tables.




I'm making some minor modifications to my home. Do I need to file drawings or obtain a permit?


Depends on your definition of "minor"! The Rules of the City of New York (RCNY) has a helpful table that describes certain scenarios that may or may not require a permit; see Section 101-14. The NYC Building Code goes into further detail and defines minor work and ordinary repairs in Section 28-105.4.2. Perhaps the most common minor modification related to a building's structure is moving or removing a wall. As per the building code, the following scenarios would require you file drawings:

  1. Any modification of a load-bearing or exterior wall.
  2. Any modification of a wall that changes the layout of a floor (adds or removes a room).
  3. Removal of 50% or more of a non-load-bearing wall.
  4. Removal of more than 45 square feet of a non-load-bearing wall.
For your safety and to avoid fines, consult a structural engineer to determine the load-bearing nature of a wall prior to any home improvement project!




I'm buying property. Should I hire a structural engineer to inspect?


Structural engineers are usually not involved in the home-buying process unless there is severe structural damage. If you're buying a home, one of the first steps is to hire a home inspector. Home inspectors look at all aspects of the home, including the visible structure, and document their findings in a report. Home inspectors who find structural abnormalities in a home typically bring this to the attention of the home buyer. When the conditions are severe or beyond their scope, home inspectors typically recommend to "consult a structural engineer". If you observe any structural abnormalities on your own, such as large cracks, sags, leaning walls or stairs, rotting wood, termite damage, or rusting steel, bring this up to your home inspector before, during, or after the home inspection to see if it requires the attention of a structural engineer. If you'd like a second opinion on a structural concern, consult a structural engineer. If you're buying a larger property, such as a commercial or residential building, it is always prudent to get an existing condition assessment (also known as a pre-purchase or due-diligence study) to protect your investment. Existing condition assessments typically involve the consultation of multiple building professionals, including structural engineers, to make sure the building will function as expected.




There's construction occurring adjacent to my property. What should I do?


As a property owner, construction occurring adjacent to your property is and should be your business. Prior to any work starting, there should be a direct line of communication between you and your neighbor on the extent of work, how long it will take, how it will affect your property, and what safety measures will be taken to monitor and protect your property. If extensive work is being done adjacent to your property (such as new building construction, demolition, the removal or addition of floors, or any foundation work), request that your neighbor cover the expenses for a professional property condition assessment of your home prior to the start of construction. This assessment is typically a thorough photographic survey of the of your home and will serve as proof, for both you and your neighbor, of the existing conditions of your property before construction began. In the event that you experience damages during construction, the existing condition survey will serve as a photographic evidence of the conditions prior to construction. If your neighbor fails to cooperate or communicate, consider hiring a lawyer. For any construction occurring outside the adjacent property, your neighbor is also responsible for safeguarding your property for the duration of the construction, which may include roof protection, safety nets, scaffolding, sidewalks sheds, etc. For NYC projects: If you believe any work is being done without approved plans, without a permit, without proper protection, or in an unsafe manner, call 311 or file a complaint online at the 311 website. If you are unsure, consult a building professional such as an architect, expediter, or strutcural engineer.





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